Seamless roaming in wireless networks

ABSTRACT

A system and method for providing a seamless transition between access points for mobile devices. The method comprises associating a unique identifier for a plurality of mobile stations with a unique identifier for a first network in an acknowledgment table, then, upon receiving a frame from a mobile station, acknowledging the reception of the frame if the frame includes the unique identifier for the mobile station and the unique identifier for the network. The transfer of operation between access points is effectuated through the use of control circuitry which transfers portions of the contents of the acknowledgement table between various access points. This has the effect that the mobile stations does not sense a change in access points and thus the roaming from a first access point to a second access point is seamless.

INCORPORATED DISCLOSURES AND RELATED APPLICATIONS

This application claims the priority of, and hereby includes by reference as if fully set forth herein, the following:

-   -   U.S. Provisional Patent Application 61/095,578, filed Sep. 9,         2008, in the name of Vaduvur BHARGHAVAN and Berend DUNSBERGEN,         titled “Seamless Roaming in Wireless Networks, assigned to the         same assignee,     -   U.S. patent application Ser. No. 11/715,287, filed Mar. 7, 2007,         in the name of Vaduvur BHARGHAVAN, Sung-Wook HAN, Joseph         EPSTEIN, Berend DUNSBERGEN, and Saravanan BALASUBRAMANIAN,         titled “Seamless Mobility in Wireless Networks”, assigned to the         same assignee,     -   which itself claims the priority of, and hereby incorporates by         reference as if fully set forth herein, the following: U.S.         patent application Ser. No. 11/298,864, filed Dec. 9, 2005, in         the name of Vaduvur BHARGHAVAN, Sung-Wook HAN, Joseph EPSTEIN,         Berend DUNSBERGEN, and Saravanan BALASUBRAMANIAN, titled         “Seamless Mobility in Wireless Networks”, and assigned to the         same assignee,     -   which itself claims the priority of, and hereby incorporates by         reference as if fully set forth herein, the following: U.S.         patent application Ser. No. 11/294,673, filed Dec. 5, 2005, in         the name of Rajendran VENUGOPALACHARY, Senthil PALANISAMY,         Srinith SARANG, and Vaduvur BHARGHAVAN, titled “Omni-Directional         Antenna Supporting Simultaneous Transmission and Reception of         Multiple Radios with Narrow Frequency Separation”, and assigned         to the same assignee.

These documents are sometimes referred to herein as the “Incorporated Disclosure” or the “Incorporated Disclosures”.

In wireless communication, devices send and receive messages without necessarily being physically coupled therefor. Wireless devices sometimes include location sensors (such as those using GPS), portable computers, mobile telephones, and the like. Portable computers with wireless communication capability sometimes are coupled to a computer network, such as the Internet or the World Wide Web. The IEEE 802.11 standards (including IEEE standard 802.11a, IEEE standard 802.11b, IEEE standard 802.11g, and IEEE standard 802.11n) include techniques for coupling wireless devices to computer communication networks. In the IEEE 802.11 standards, wireless devices seek out and select “access points”, also called “AP's”. Each wireless device associates itself with a particular AP, with which it communicates. Each wireless device, such as a mobile station, also called an “STA” (which might be moving), determines from time to time whether it has good communication with its associated AP, and whether it would have better communication with a different AP.

Access points exhibit a known deficiency when an STA moves beyond the effective range of an AP, because the STA needs to re-establish communication with a new AP, a process called “handoff”. Handoff problems include loss of signal and decrease in QoS (Quality of Service). For applications requiring high QoS, such as digitally transmitting audio information, the latency time of the handoff can be uncomfortably perceptible to a human listener.

SUMMARY

Techniques, including apparatuses and methods for seamless transitions between AP's include associating a station UID (unique identifier) for a set of mobile stations, with a network UID for a 1^(st) network in an acknowledgment table. Upon receiving a frame from a mobile station in that set of mobile stations, reception of the frame is acknowledged only if the frame includes both the station UID for the mobile station and the network UID for the network. This has the effect that mobile stations might be associated with selected networks (and selected AP's), without troubling those AP's or their control hardware or software.

Transfer of a station's operation between AP's (i.e., handoff) is performed by transferring one or more portions of acknowledgment tables among AP's. This has the effect that AP's collectively know which AP is associated with that mobile station, and collectively respond to that mobile station only by its associated AP. This has the effect that when the AP's collectively (e.g., in response to a controller as described in the Incorporated Disclosures) determine that the mobile station should be transferred from a 1^(st) AP to a 2^(nd) AP, the mobile station does not sense a change in AP's, with the effect that any transfer from a 1^(st) AP to a 2^(nd) AP is substantially seamless to users of the mobile station.

This has the effect that AP's (or their controller, as described in the Incorporated Disclosures), determine to which AP each mobile station is associated, rather than the reverse (as generally specified by the IEEE standard protocols). In general, AP's and their controller are in a better position to determine to which AP a mobile station should be associated. Moreover, there is no particular requirement for a particular mobile station to undergo a time-consuming process of handoff when that mobile station should, from time to time, be associated with a different AP. This has the effect that the mobile station can be transferred between a 1^(st) AP and a 2^(nd) AP without troubling the mobile station, without even letting the mobile station know that the transfer has taken place, and without substantial latency in making the transfer.

DETAILED DESCRIPTION Generality of Invention

This application should be read in its most general possible form. For example and without limitation:

-   -   References to specific techniques include alternative and more         general techniques, especially when discussing new aspects of         the technologies, or how the invention might be made or used.     -   References to “preferred” techniques generally mean that the         inventors contemplate using those techniques in a suitable         context, for example and without limitation, a commercial         context, and think they are best for that contemplated context.         This explicitly does not exclude other and further techniques         for making or using the invention, and does not mean that the         described techniques are necessarily essential or that they         would be preferred in all contexts.     -   References to contemplated causes and effects for some         implementations do not preclude other causes or effects that         might occur in other implementations.     -   References to reasons for using particular techniques do not         preclude other reasons or other techniques, even if completely         contrary, where circumstances would indicate that the stated         reasons or techniques are not as applicable.     -   References to particular examples of techniques by which the         invention might be made, used, or otherwise employed, do not         preclude other examples or other techniques, even if completely         contrary. After reading this application, those skilled in the         art will recognize many other variations which are possible,         which remain within the content, scope and spirit of the         invention, and which would not require undue experimentation or         new invention.

DEFINITIONS

This application should be read with these definitions in mind. These definitions are intended to show the most general form of the invention, and not to be restrictive in any way:

-   -   The phrase “access point”, the term “AP”, and the like,         generally refer to devices capable of wireless communication         with wireless devices and capable of either wired or wireless         communication with other devices. The term “AP's”, and the like,         generally refers to a set of one or more such devices. For         example, AP's might communicate with external devices using a         L2/L3 network. However, in the context of the invention, there         is no particular requirement that AP's have an actual wired         communication link; AP's might communicate entirely wirelessly         themselves.     -   The phrases “incoming message”, “received frame”, and the like,         generally refer to a message packet or message frame sent by a         wireless device or wireless station to one or more AP's, and         received at a particular AP. Received frames might be sent by a         wireless station to one or more AP's using one or more of the         IEEE 802.11 wireless communication standards, some similar one         or more standards, or some other one or more standards. The         incoming message may be a unicast frame (i.e., intended for a         single AP) or a multicast frame (i.e., intended for a set of,         possibly multiple, AP's).     -   The phrases “outgoing message” and “transmit frame”, and the         like, generally refer to a message packet or message frame being         sent to one or more wireless devices or stations from an AP.         Transmit frames might be sent from an AP using one or more of         the IEEE 802.11 wireless communication standards, some similar         one or more standards, or some other one or more standards. The         incoming message may be a unicast frame (i.e., intended for a         single AP) or a multicast frame (i.e., intended for a set of,         possibly multiple, AP's).     -   The phrase “wireless communication”, and the like, generally         refers to radio frequency or other electromagnetic         communication. Wireless communication might make use of a         wireless communication standard such as one or more of IEEE         standards 802.11a, 802.11b, 802.11g, or 802.11n, some similar         one or more standards, or some other one or more standards.         However, in the context of the invention, there is no particular         requirement that wireless communication or a communication         network must necessarily (1) use radio spectrum, (2) use         electromagnetic communication, or even (3) be entirely confined         to untethered communication coupling. For examples, wireless         communication might use sonic waves, possibly including         ultrasound, or wireless communication might make use of both         wired and unwired communication paths.     -   The phrases “wireless device”, “wireless station”, “mobile         station” and the like, (“STAs”) generally refer to devices         capable of wireless communication with AP's. These devices need         not be mobile, such as for example a desktop computer with         wireless capability. Wireless communication might make use of a         wireless communication standard such as one or more of IEEE         standards 802.11a, 802.11b, 802.11g, or 802.11n, some similar         one or more standards, or some other one or more standards.         However, in the context of the invention, there is no particular         requirement that one or more of these particular communication         standards are used, e.g., the wireless communication might be         conducted according to a standard other than an IEEE 802.11         standard, or even according to standard other than an IEEE         standard entirely. Moreover, in the context of the invention,         there is no particular requirement that all, or even a         designated subset of, wireless devices use the same standard, or         that such wireless devices even use inter-compatible         communication standards.     -   Digital communications devices might operate using a multi-layer         configuration, such as for example one including Application,         Presentation, Session, Transport, Network, Data Link, and         Physical layers. The term “layer”, and the like, generally         refers to a collection of related functions that provides         services to one or more layers above it and receives services         from one or more layers below it in a designated ordering. For         example, a layer that provides error-free communications across         a network might provide a path useful to applications above it,         while that layer that provides error-free communications across         a network might make use of one or more lower layers to send and         receive packets that make up the contents of the path.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a table illustrating an acknowledgment table (“ACK Table”) as might be found in a memory device of an access point, or in the control circuitry of a wireless Communications device (i.e., a mobile device), according to an embodiment.

FIG. 2 is a table illustrating the beginning of a typical frame format for use in the IEEE 802.11 communications protocol, according to an embodiment.

FIG. 3 is a block diagram illustrating access points sharing a BSSID for a mobile station, according to an embodiment.

FIG. 4 is a block diagram illustrating access points utilizing a per station BSSID, according to an embodiment.

ACK Table Operation

FIG. 1

FIG. 1 illustrates an acknowledgment table (“ACK Table”) as might be found in a memory device of an access point, or in the control circuitry of a wireless communications device (i.e., a mobile device). The ACK Table as shown provides for a data structure relating a station unique identifier such as a media access control (MAC) address of a mobile station to a basic service set identifier (BSSID), sometimes called herein a “network unique identifier” of a network. However, in the context of the invention, there is no particular requirement that these particular data items are used. Other, further, or distinct data elements might be used to match mobile stations with their associated networks.

A BSSID is used to identify one or more IEEE 802.11 wireless LAN's with which a mobile station attempts to communicate. An example of at least one vendor's implementation of an ACK Table implemented in a communications chip set is implemented and shown in Broadcom models 4342, 4322 and 4387. Other devices may have this same or a similar capability, whether or not from the same vendor.

In the ACK Table shown in the FIG. 1, a MAC address represents the physical address of a mobile device disposed for being connected to a network, generally expressed as a 48-bit hexadecimal number (i.e., 6 octets). Wireless networks are often included in a multi-layer configuration that allows for operation between hierarchies of systems. The MAC layer is generally a sublayer, as defined by the IEEE standard 802 protocols, of a networking layer. The MAC sublayer is responsible for delivering error-free data between two computers on the network.

Mobile stations are each associated with a station unique identifier, which is itself associated with a network unique identifier, the latter including a unique BSSID the mobile station might access, which is itself associated with one or more particular networks in a wireless communication system. This has the effect that the mobile station can access those particular networks, and no others. The mobile station's unique BSSID access ability might be moved from a 1^(st) AP to a 2^(nd) AP when reassigning the mobile station from the 1^(st) AP to the 2^(nd) AP. As only those AP's with the MAC address of the mobile station in their ACK Table will respond to the mobile station, the one or more AP's maintaining that unique BSSID are the only AP's that respond to message packets from the mobile station. While such AP's might be only one designated such AP at any particular time, in the context of the invention, there is no particular requirement for this restriction, and in fact, during transfer of a mobile station from a 1^(st) AP to a 2^(nd) AP, there will generally be at least some time during which the MAC address for that AP is present in the ACK Tables for each of the 1^(st) AP and the 2^(nd) AP. As the one or more AP's maintaining that unique BSSID are the only AP's that respond to message packets from that particular mobile station, this has the effect of limiting access by that particular mobile station to only networks available to those one or more AP's maintaining that unique BSSID.

FIG. 2

FIG. 2 shows the beginning of a typical frame format for use in the IEEE 802.11 communications protocol. Not all fields are necessarily present in every frame. Frame communication between the same devices may have different frame formats at different stages of the communication process. This may include changing frame formats between communication layers within a wireless communication device.

In operation, distinct receive frames might require differing responses or acknowledgments. For example and without limitation, a unicast MAC Protocol Data Unit (MPDU or MMPDU) receive frame generally requires, according to the IEEE 802 protocol standards, an ACK frame response. Other receive frames may require more efficient forms of acknowledgment such as BLOCK-ACK frames. Upon reception of a frame requiring an ACK, each AP receiving that frame will search its ACK Table for an entry where a MAC address matches a BSSID supported in the AP. Only if the received frame requires a response and a matching entry is found, will the AP respond with the appropriate response. The response type is based on the received frame.

Upon reception of a frame requiring an ACK, each AP receiving that frame will search its ACK Table for an entry where both the Address₁ matches the BSSID and the Address₂ matches the MAC address. Only if the received frame requires a response and a matching entry is found, will the AP respond with the appropriate response. The response type is in response to the received frame.

Shared BSSID

FIG. 3

FIG. 3 shows a functional block diagram of a sharing a BSSID. Mobile stations are configured to attempt to find available AP's for communication. Processors in the mobile stations evaluate factors for connections and make independent roaming decisions to make sure they are connected to the best AP. In preferred embodiments the mobile stations roam seamlessly across AP's because the roaming decisions are made by the infrastructure (APs and a controller). This has the effect that all handoffs between different APs are completely transparent to the mobile stations.

To effectuate seamless roaming, a 1^(st) access point AP, contains an ACK Table as described above. The ACK Table contains both mobile station MAC addresses and BSSIDs and is coupled to one or more mobile stations. For the transition of STA₂ from AP₁ to AP₂, both AP₁ and AP₂ support the same BSSID (BSSID₁). By creating a shared media environment with the same BSSID, both AP's can receive the same frame from STA₂. However, through the operation of the ACK Table, only the AP that has a complete matching entry in the ACK Table will respond to the STA. Before the transition, only AP, has complete information for STA₂. This has the effect that STA₂ transitions from AP₁ to AP₂ transparently because the STA does not sense that a different AP has taken over the communications link. Communication and coordination between the APs is preformed through the operation of the controller (not shown), which effects the proper ACK Table for each AP.

Per Station BSSID

FIG. 4

FIG. 4 shows a functional block diagram of using a per station BSSID. In the FIG. 4 an access point AP₁ is constructed with an ACK Table having a MAC address for each mobile station and an associated BSSID for each mobile station. To effectuate seamless roaming, the BSSID from the 1^(st) AP (AP₁) is transferred to the 2^(nd) AP (AP₂) during the transition. The transfer is effectuated by a controller (not shown). Through the operation of the ACK Table, only the AP that has a complete matching entry in the ACK Table will respond to the STA. Before the transition, only AP₁ has complete information for STA₂. During the transition, AP₂ receives complete ACK Table information relating to STA₂. After the transition, only AP₂ has complete ACK Table information for STA₂. This has the effect that STA₂ transitions from AP₁ to AP₂ transparently because the STA does not sense that a different AP has taken over the communications link. Communication and coordination between the AP's is performed through the operation of the controller, which effects the proper ACK Table for each AP.

Alternative Embodiments

The invention has applicability and generality to other aspects of wireless communication, and is not limited to wireless communication based upon IEEE 802.11 standards. After reading this application, those having skill in the art would recognize that the systems and methods disclosed herein my be effectuated using other techniques. For example and without limitation, the transmission time might be provided by the physical layer or data link layer to a higher level for determining the transmission time.

After reading this application, those skilled in the art would recognize that the scope and spirit of the invention include other and further embodiments beyond the specifics of those technologies disclosed herein, and that such other and further embodiments would not require undue experimentation or new invention. 

The invention claimed is:
 1. A computer-implemented method performed by an access point of a plurality of access points managed by a controller of a wireless communication network the method comprising the steps of: associating a mobile station of a plurality of mobile stations with the access point by storing, at both the mobile station and the access point, a persistent, uniquely assigned BSSID (Basic Service Set Identifier) that is uniquely assigned to the mobile station among a plurality of persistent uniquely-assigned BSSIDs stored at the access point that are assigned to the plurality of mobile stations, wherein each of the plurality of access points independently using layer 2 communications and the persistent, uniquely-assigned BSSID is configured in the mobile station by the access point with a beacon frame or a probe response frame sent from the mobile station to the access point; receiving a frame from the mobile station, the frame comprising a sender address defined by a MAC address unique to the mobile station and a receiver address defined by the persistent, uniquely-assigned BSSID; responsive to matching the receiver address of the received frame to one of the stored plurality of persistent, uniquely-assigned BSSIDs, generating an ACK frame to send to the mobile station; and responsive to a handoff of the mobile station from the access point to another access point of the plurality of access points, disassociating the mobile station from the access point by deleting the persistent, uniquely-assigned BSSID, wherein the another access point associates with the mobile station by storing the persistent, uniquely-assigned BSSID allowing the mobile station to seamlessly continue to store and use the same persistent, uniquely-assigned BSSID for communication with the wireless communication network.
 2. The method of claim 1, further comprising: receiving the persistent, uniquely-assigned BSSID from the controller assigning the mobile station to the access point.
 3. The method of claim 1, further comprising: receiving a message from the controller disassociating the mobile station from the access point.
 4. The method of claim 1, further comprising: responsive to not matching the receiver address of the received frame to one of the stored BSSIDs, ignoring the received frame.
 5. A non-transitory computer readable medium storing a computer program product that, when executed by a processor performs a method in an access point of a plurality of access points managed by a controller of a wireless communication network the method comprising the steps of: associating a mobile station of a plurality of mobile stations with the access point by storing, at both the mobile station and the access point, a persistent, uniquely assigned BSSID (Basic Service Set Identifier) that is uniquely assigned to the mobile station among a plurality of persistent uniquely-assigned BSSIDs stored at the access point that are assigned to the plurality of mobile stations, wherein each of the plurality of access points independently using layer 2 communications and the persistent, uniquely-assigned BSSID is configured in the mobile station by the access point with a beacon frame or a probe response frame sent from the mobile station to the access point; receiving a frame from the mobile station, the frame comprising a sender address defined by a MAC address unique to the mobile station and a receiver address defined by the persistent, uniquely-assigned BSSID; responsive to matching the receiver address of the received frame to one of the stored plurality of persistent, uniquely-assigned BSSIDs, generating an ACK frame to send to the mobile station; and responsive to a handoff of the mobile station from the access point to another access point of the plurality of access points, disassociating the mobile station from the access point by deleting the persistent, uniquely-assigned BSSID, wherein the another access point associates with the mobile station by storing the persistent, uniquely-assigned BSSID allowing the mobile station to seamlessly continue to store and use the same persistent, uniquely-assigned BSSID for communication with the wireless communication network.
 6. The at least one computer readable product of claim 5, further comprising: receiving the persistent, uniquely assigned BSSID from the controller assigning the mobile station to the access point.
 7. The at least one computer readable product of claim 5, further comprising: receiving a message from the controller disassociating the mobile station from the access point.
 8. The at least one computer readable product of claim 5, further comprising: responsive to not matching the receiver address of the received frame to one of the stored persistent, uniquely-assigned BSSIDs, ignoring the received frame.
 9. The at least one computer readable product of claim 5, further comprising: receiving the persistent, uniquely assigned BSSID from the controller assigning the mobile station to the access point.
 10. An access point of a plurality of access points managed by a controller of a wireless communication network, comprising: a processor; and a memory coupled to the processor and containing program code, which when executed cause the processor to: associate a mobile station of a plurality of mobile stations with the access point by storing, at both the mobile station and the access point, a persistent, uniquely assigned BSSID (Basic Service Set Identifier) that is uniquely assigned to the mobile station among a plurality of persistent uniquely-assigned BSSIDs stored at the access point that are assigned to the plurality of mobile stations, wherein each of the plurality of access points independently using layer 2 communications and the persistent, uniquely-assigned BSSID is configured in the mobile station by the access point with a beacon frame or a probe response frame sent from the mobile station to the access point; receive a frame from the mobile station, the frame comprising a sender address defined by a MAC address unique to the mobile station and a receiver address defined by the persistent, uniquely-assigned BSSID; responsive to matching the receiver address of the received frame to one of the stored plurality of persistent, uniquely-assigned BSSIDs, generate an ACK frame to send to the mobile station; and responsive to a handoff of the mobile station from the access point to another access point of the plurality of access points, disassociate the mobile station from the access point by deleting the persistent, uniquely-assigned BSSID, wherein the another access point associates with the mobile station by storing the persistent, uniquely-assigned BSSID allowing the mobile station to seamlessly continue to store and use the same persistent, uniquely-assigned BSSID for communication with the wireless communication network. 